diff --git a/.github/workflows/spack.yml b/.github/workflows/spack.yml
index 63fb34d7..52ac0f7e 100644
--- a/.github/workflows/spack.yml
+++ b/.github/workflows/spack.yml
@@ -12,8 +12,9 @@ jobs:
       - name: grab spack
         uses: actions/checkout@v4
         with:
-          repository: spack/spack
-          path: ./spack
+          repository: 'spack/spack'
+          ref: 'v0.21.1'
+          path: './spack'
 
       - name: spack test drive
         run: |